Fixed focal balloon for interactive angioplasty and stent implantation catheter with focalized balloon

ABSTRACT

Disclosed is a focal balloon having at least one reference zone and a focal zone. In one embodiment, the reference zone and focal zone are inflatable to a first generally cylindrical profile at a first pressure. At a second, greater pressure, the focal section expands to a second, greater diameter, while the reference zone remains substantially at the first diameter. In an alternate embodiment, the focal zone and the reference zone are inflatable to their respective predetermined diameters at the inflation pressure, in the absence of constricting lesions or anatomical structures. Both balloons may be utilized to conduct interactive angioplasty to provide real-time feedback about the morphology of the lesion, and both balloons may be utilized to implant or size intravascular stents.

The present application is a continuation of Ser. No. 02/640,533, filedMay 2, 1996, entitled Fixed Focal Balloon for Interactive Angioplastyand Stent Implantation, now U.S. Pat. No. 5,645,560, which is acontinuation in part of application Ser. No. 02/572,783, filed Dec. 15,1995, now abandoned, which is a continuation in part of application Ser.No. 02/201,335, filed Feb. 24, 1994, entitled Variable Diameter BalloonDilatation Catheter, now U.S. Pat. No. 5,470,313.

BACKGROUND OF THE INVENTION

The present invention relates to catheters for insertion into a bodylumen. More particularly, the present invention relates to a "focal"balloon dilatation catheter for use in the vascular system. In addition,the present invention relates to interactive angioplasty methods ofusing focal and differential compliance balloons.

Prior art vascular dilatation balloons on typical dilatation catheterstend to fall into one of two broad classes. Most are considerednoncompliant balloons, formed from a generally nondistensible materialsuch as polyethylene. The perceived advantage of the noncompliantballoons is that they exhibit a substantially uniform exterior inflatedprofile which remains substantially unchanged upon incremental increasesin inflation pressure. In theory, noncompliant balloons are advantageousbecause they allow the introduction of increased inflation pressure tobreak particularly calcified lesions, yet retain a predictable inflatedprofile so that damage to the surrounding native lumen is minimized.

Certain compliant balloons are also known in the art. A compliantballoon is one which is able to grow in diameter in response toincreased inflation pressure. One difficulty with compliant balloons,however, is that inflation within a difficult lesion can cause theballoon to inflate around the plaque to produce a generallyhourglass-shaped inflated profile. This can result in damage to thenative vessel adjacent the obstruction, while at the same time failingto sufficiently alleviate the stenosis.

In use, both the compliant and noncompliant balloons are generallyinflated within a vascular stenosis to a rated inflation pressure. Theballoon may be subsequently inflated to a higher inflation pressure ifthat is desirable in the clinician's judgment. However, the clinicianhas no effective way to assess the actual inflated diameter of theballoon in vivo based upon the unconstrained in vitro balloonspecifications. The in vivo expansion characteristics of the balloon maytrack or deviate from the in vitro specifications depending upon themorphology of the lesion and the appropriateness of the selected balloonsize. The clinician may know only generally or not at all the degree ofcalcification of the lesion, the symmetry or asymmetry, whether thelesion is soft or resilient, or other variations which affect inflation.In applications where a relatively accurate inflated diameter isdesired, such as in certain dilatations or in the implantation oftubular stents, the clinician using prior dilatation balloons thus maynot have enough information about the dilatation characteristics of aparticular lesion to optimize the dilatation or stent implantationprocedure.

Therefore, there exists a need in the art for a vascular dilatationcatheter with a balloon which is able to grow predictably in response toincreased inflation pressure, and the expansion of which the cliniciancan observe in real time in comparison to a known diameter reference.

SUMMARY OF THE INVENTION

There is provided in accordance with one aspect of the present inventiona method of determining the inflated diameter of a treatment site in abody lumen. The method comprises the steps of providing a catheterhaving an elongate flexible tubular body and an inflatable balloon onthe body. The balloon has at least one reference zone inflatable to afirst diameter, and a focal zone inflatable to a second, largerdiameter.

The catheter is positioned within a body lumen so that the focal zone ispositioned adjacent a treatment site. Inflation of the balloon iscommenced, and the clinician observes the diameter of the focal zonecompared to the reference zone. The balloon is inflated to a sufficientpressure to advance the focal zone to the second diameter, and theinflation pressure at which the focal zone inflates to the seconddiameter is observed. Inflation to the second diameter is observable bycomparing the visually apparent diameter of the focal zone with respectto the reference zone. The observed pressure is then compared topredetermined inflation characteristic values for the balloon, todetermine the diameter of the balloon in the focal zone at the treatmentsite at the observed inflation pressure.

In accordance with another aspect of the present invention, there isprovided a method treating a site in a body lumen. The method comprisesthe steps of providing a catheter having an elongate flexible tubularbody and a dilatation balloon on the body. The balloon is inflatable toan inflation profile wherein at least one reference segment isinflatable to a first diameter and a focal segment of the balloon isinflatable to a second, greater diameter.

The catheter is positioned within a body lumen so that the balloon isadjacent a treatment site. The balloon is then inflated to a firstinflation pressure, wherein the reference and the focal segments areexpected to inflate to the inflation profile.

The actual inflation profile of the balloon at the first inflationpressure is observed, and the observed inflation profile is compared tothe expected inflation profile at the first inflation pressure.Subsequent treatment is selected in response to the comparison of theactual inflation profile at the first inflation pressure to the expectedprofile at the first inflation pressure.

Further features and advantages of the present invention will becomeapparent to one of skill in the art in view of the Detailed Descriptionof Preferred Embodiments which follows, when considered together withthe attached drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a preferred embodiment of a variablediameter inflation catheter of one aspect of the present invention, inthe second inflation configuration.

FIG. 2 is a partial cross-sectional view of a preferred embodiment ofthe variable diameter inflation catheter at a first inflation profile.

FIG. 3 is a partial cross-sectional view of a preferred embodiment ofthe variable diameter inflation catheter at a second inflation profile.

FIG. 4 is a schematic view of the embodiment of FIG. 1, shown in thefirst inflation configuration.

FIG. 5 illustrates a comparison of compliance curves between thereference zones and the focal zone as a function of increased inflationpressure in a differential compliance focal balloon of the presentinvention.

FIG. 6 is a schematic illustration of a balloon of the present inventionhaving a relatively thin wall in the focal section.

FIG. 7 is a cross sectional schematic illustration of a fixed focalballoon catheter of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is disclosed a variable diameter inflationcatheter 10 in accordance with of one aspect of the present invention.Catheters embodying additional features known in the vascular dilatationart, such as implantable stents, drug delivery, perfusion and dilatationfeatures, or any combination of these features, can be used incombination with the focal balloon of the present invention as will bereadily apparent to one of skill in the art in view of the disclosureherein.

The catheter 10 generally comprises an elongate tubular body 12extending between a proximal control end 14 and a distal functional end16. The length of the tubular body 12 depends upon the desiredapplication. For example, lengths in the area of about 120 cm to about140 cm are typical for use in percutaneous transluminal coronaryangioplasty applications.

The tubular body 12 may be produced in accordance with any of a varietyof known techniques for manufacturing balloon-tipped catheter bodies,such as by extrusion of appropriate biocompatible plastic materials.Alternatively, at least a portion or all of the length of tubular body12 may comprise a spring coil, solid walled hypodermic needle tubing, orbraided reinforced wall, as is understood in the catheter and guide wirearts.

In general, tubular body 12, in accordance with the present invention,is provided with a generally circular cross-sectional configurationhaving an external diameter within the range of from about 0.03 inchesto about 0.065 inches. In accordance with one preferred embodiment ofthe invention, the tubular body 12 has an external diameter of about0.042 inches (3.2 f) throughout most of its length. Alternatively,generally triangular or oval cross-sectional configurations can also beused, as well as other non-circular configurations, depending upon thenumber of lumen extending through the catheter, the method ofmanufacture and the intended use.

In a catheter intended for peripheral vascular applications, the tubularbody 12 will typically have an outside diameter within the range of fromabout 0.039 inches to about 0.065 inches. In coronary vascularapplications, the tubular body 12 will typically have an outsidediameter within the range of from about 0.026 inches to about 0.045inches. Diameters outside of the preferred ranges may also be used,provided that the functional consequences of the diameter are acceptablefor the intended purpose of the catheter. For example, the lower limitof the diameter for tubular body 12 in a given application will be afunction of the number of fluid or other functional lumen, supportstructures and the like contained in the catheter, and the desiredstructural integrity.

Tubular body 12 must have sufficient structural integrity (e.g.,"pushability") to permit the catheter to be advanced to distal arteriallocations without buckling or undesirable bending of the tubular body12. The ability of the body 12 to transmit torque may also be desirable,such as in embodiments having a drug delivery capability on less thanthe entire circumference of the delivery balloon. Larger diametersgenerally have sufficient internal flow properties and structuralintegrity, but reduce perfusion in the artery in which the catheter isplaced. Increased diameter catheter bodies also tend to exhibit reducedflexibility, which can be disadvantageous in applications requiringplacement of the distal end of the catheter in a remote vascularlocation. In addition, lesions requiring treatment are sometimes locatedin particularly small diameter arteries, necessitating the lowestpossible profile.

As illustrated schematically in FIG. 1, the distal end 16 of catheter 10is provided with at least one inflation balloon 18 having a variablediameter. The proximal end 14 of catheter 10 is provided with a manifold20 having a plurality of access ports, as is known in the art.Generally, manifold 20 is provided with a guide wire port 22 in an overthe wire embodiment and a balloon inflation port 24. Additional accessports are provided as needed, depending upon the functional capabilitiesof the catheter 10. The balloon 18 can also be mounted on a rapidexchange type catheter, in which the proximal guidewire port 22 would beunnecessary as is understood in the art. In a rapid exchange embodiment,the proximal guidewire access port is positioned along the length of thetubular body 12, such as between about 4 and about 20 cm from the distalend of the catheter.

Referring to FIGS. 2 and 3, the two-step inflation profile of theinflation balloon 18 is illustrated. In FIG. 2, the balloon 18 isillustrated at a first inflation profile, in which in an unconstrainedexpansion it exhibits a substantially cylindrical central workingprofile. The dimensions in FIG. 2 are exaggerated to illustrate aproximal segment 26 and a distal segment 28 which are axially separatedby a central focal segment 30. However, as will be understood by one ofordinary skill in the art, when the balloon 18 is inflated to the firstinflation profile, the exterior of the balloon 18 preferably exhibits asubstantially smooth cylindrical working profile.

In FIG. 3, the inflation balloon 18 is illustrated at a second inflationprofile. The proximal segment 26 and the distal segment 28 of theballoon are separated by the central focal segment 30 having a greaterdiameter. The configuration of FIG. 2 is achieved by inflating theballoon 18 to a first inflation pressure, while the configuration ofFIG. 3 is achieved by increasing the inflation pressure to a second,higher pressure as will be discussed below.

The details of one preferred embodiment of the variable diameterinflation catheter 10 are discussed with reference to FIGS. 2 and 3.Preferably, the tubular body 12 is provided with at least a guidewirelumen 32 extending all the way through the balloon 18, and an inflationlumen 34 extending into the proximal end of the balloon 18.

In the illustrated embodiment, an inner balloon 36 is disposed coaxiallywithin an outer balloon 38. A substantially nondistensible expansionlimiting band 40 is disposed in between the balloons 36 and 38 adjacenta proximal annular shoulder 42, to limit the radial expansion of theballoon 18. Similarly, a distal expansion limiting band 44 is disposedbetween the inner balloon 36 and outer balloon 38 adjacent a distalannular shoulder 46.

Expansion limiting bands 40 and 44 or other inflation limitingstructures can be provided in any of a variety of ways which will bewell-understood by one of skill in the art in view of the disclosureherein. For example, in one embodiment, the bands 40 and 44 eachcomprise a tubular section of polyester, each having an axial length ofabout 5 mm, a diameter of about 2.5 mm and a wall thickness of about0.0003 inches. Other generally nondistensible materials such as nylon,polyamide, Kevlar fiber, cross-linked polyethylene, polyethyleneterephthalate and others, may be utilized to accomplish theexpansion-limiting effect.

The expansion limiting characteristics can be achieved by the additionof a structure that is discrete from the balloon, or by modifying theexpansion properties of the balloon material itself. For example, theballoon can be provided with zones of differing wall thickness, or zoneshaving different levels of cross linking as will be discussed.

In general, the bands 40 and 44 must be of a sufficient thickness orstructural integrity for the particular material used to substantiallywithstand inflation under the pressures normally utilized in the contextof dilatation catheters. However, the bands 40 and 44 are preferablythin enough to provide a substantially smooth exterior surface of theballoon 18.

Preferably, as illustrated in FIGS. 2 and 3, the expansion-limitingbands 40 and 44 are sandwiched between the inner balloon 36 and theouter balloon 38. In alternative embodiments, the expansion-limitingbands 40 and 44 or other inflation limiting structures may be coated ormounted on the exterior surface of the balloon 18, the interior surfaceof the balloon 18 or within the wall of the balloon 18. Balloon 18 canbe provided with two or more layers as illustrated, or with only asingle layer as will be discussed.

The axial length of the bands 40 and 44 can be varied widely dependingupon the dimensions and the objectives of the catheter 10 as will beapparent to one of ordinary skill in the art. Further, the proximal band40 and distal band 44 need not be of similar lengths. In general,however, some examples of dimensions which are useful in the coronaryangioplasty dilatation environment are reproduced in Table 1 below, inwhich A represents the axial length of the balloon 18 between proximalshoulder 42 and distal shoulder 46, B represents the axial distancebetween distal shoulder 46 and transition point 48, and C represents theaxial length of the central focal segment 30. The dimensions of Table 1are exemplary only, and the present invention can be accomplished usinga wide variety of other dimensions as will be apparent to one of skillin the art.

                  TABLE 1                                                         ______________________________________                                        A              B                C                                             ______________________________________                                        20 mm          5 mm             10 mm                                         30 mm          5 mm             20 mm                                         40 mm          5-10 mm          20-30 mm                                      ______________________________________                                    

The catheter 10 illustrated in FIGS. 2 and 3 can be manufactured inaccordance with any of a variety of techniques which will be appreciatedby one of ordinary skill in the art in view of the disclosure herein. Inthe following disclosure, particular materials and dimensions will beused as an example only, and other dimensions and materials can beselected depending upon the desired characteristics of the finishedproduct.

In one particular method of manufacturing, a low density polyethyleneextrusion stock tube having an inside diameter of about 0.018 inches andan outside diameter of about 0.043 inches is used for the inner andouter balloons 36, 38.

The polyethylene stock tubing is cross-linked by exposure to an electronbeam in accordance with techniques well known in the art. A test segmentof the cross-linked stock tubing is free blown up to 3.0 mm in diameter.If the cross-linked stock tubing can be free blown to a diameter greaterthen 3.0 mm, the stock tubing is cross-linked again and retested untilthe desired free blow diameter is achieved.

The appropriately cross-linked stock tubing is then blown to a diameterof 2.5 mm within a teflon capture tube (not shown) which acts to moldthe balloon to its desired first inflation diameter. The teflon capturetube is a generally tubular body which has approximately the same insidediameter as the desired inflation diameter of the balloon. The tefloncapture tube is heated by any of a number of heating means such aselectric coils or a furnace to a temperature which is sufficient to moldthe balloon to the desired inflation diameter. In this case, thecross-linked polyethylene balloon is preferably heated to a temperatureof about 300° F. The teflon chamber is then cooled to a temperaturebelow the softening temperature of the balloon. Once cooled, the balloonis deflated and removed from the capture tube.

A section of inflation balloon material is thereafter stretched withapplication of heat to neck down the proximal and distal ends 37, 39 toa thickness of about 0.001 inches and a diameter which relativelyclosely fits the portion of the tubular catheter body 12 to which it isto be sealed.

The balloon is then attached to the tubular body 12 by any of a varietyof bonding techniques known to one of skill in the art such as solventbonding, thermal adhesive bonding or by heat shrinking/sealing. Thechoice of bonding techniques is dependent on the type of balloonmaterial and tubular body material used to form the catheter 10.

In one particular method of manufacture, inner balloon 36 and outerballoon 38 are attached to the catheter body 10. The proximal necked end37 of the inner balloon 36 is heat sealed around the catheter body 12.The distal necked end 39 of the inner balloon 36 is thereafter heatsealed around the distal end 16 of the catheter body 12. In general, thelength of the proximal end 37 and the distal end 39 of the inner balloon36 which is secured to the catheter body 12 is within the range of fromabout 3 mm to about 10 mm, however the proximal and distal balloonnecked ends 37, 39 are as long as necessary to accomplish theirfunctions as a proximal and distal seal.

Expansion limiting bands 40 and 44 are respectively positioned at theproximal segment 26 and the distal segment 28 of the inner balloon 36and may be bonded or otherwise secured to the inner balloon 36. Theouter balloon 38 is thereafter be mounted to the catheter body 12 in asimilar manner as the inner balloon 36, following "necking down" of theproximal and distal axial ends of the outer balloon 38 by axialstretching under the application of heat. The outer balloon 38 isadvanced axially over the inner balloon 36 and the expansion limitingbands 40 and 44. The outer balloon 38 may thereafter be bonded to theinner balloon 36, and to the expansion limiting bands 40 and 44 by anyof a variety of bonding techniques such as solvent bonding, thermaladhesive bonding or by heat sealing also depending on the type ofballoon material used. Alternatively, the expansion limiting bands aresimply entrapped between the balloons without any bonding or adhesion.

In a preferred embodiment, the inner balloon and the outer balloon 36,38 are both cross-linked polyethylene balloons which are difficult tobond together using conventional solvents. If sealing is desired, theinner balloon 38 and the outer balloon 38 are heat sealed together asdescribed below. In another embodiment, the inner balloon 36 and outerballoon 38 are secured together through the use of a UV-curableadhesive.

The inner balloon 36 and the outer balloon 38, once mounted to thecatheter body 12, can be heat sealed together in a heating chamber (notshown) such as a Teflon capture tube. Inner balloon 36 and outer balloon38 are inflated in the chamber until the inner balloon and the outerballoon inflate to the first inflation diameter. The heating chamber isheated by any of a number of heating means such as electric coils or afurnace to heat air to a temperature which is sufficient to bond the twoballoons 36, 38 together. In this case, the cross-linked polyethyleneballoons are preferably heated to a temperature of about 300° F. withinthe chamber which causes both balloons 36, 38 to seal together to form adouble walled variable diameter inflation balloon 18. The chamber isthen cooled to a temperature below the softening temperature of theinner and outer balloons 36 and 38. Once cooled, the variable diameterballoon 18 is deflated and the catheter 10 is removed from the chamber.

It will be apparent to one of skill in the art, that it is possible toattach the inner balloon 36 and the outer balloon 38 to the catheterbody 12 without adhesively bonding or otherwise securing the twoballoons together. In this case, the two balloons will respond to theapplied inflation pressure with the inner balloon 36 forcing the outerballoon 38 to simultaneously inflate both balloons 36, 38. The expansionlimiting bands 40 and 44 can be merely sandwiched between the innerballoon 36 and the outer balloon 38 and do not in this embodiment needto be bonded to either balloon.

The variable diameter balloon design of the present invention can alsobe accomplished with a single layer balloon or a double layer balloonwithout the inclusion of additional expansion limiting bands. This isaccomplished by decreasing the relative compliance of the zones of theballoon that are intended to remain at the first inflated diameter.Alternatively, the compliance of the focal section can be increasedrelative to that of the reference zones.

For example, polyethylene extrusion stock is cross-linked to 3.0 mm andblown into a mold of a diameter of about 2.5 mm as described above toform a balloon. Balloon stock can be crosslinked either before or aftermounting on the catheter, and in either the inflated or deflated state.The proximal and distal segments 26, 28 of the balloon on the catheter10 are masked such as with steel clamps or other masks known in the artto block electron beam penetration, leaving the central segment 30 ofthe balloon exposed. The central segment 30 of the balloon 18 is exposedagain to an electron beam source to be further cross-linked at the 2.5mm diameter. Balloons manufactured in this manner have been found toexhibit a relatively highly compliant central zone and relatively lesscomplaint axial end zones in a manner that achieves the two-stepdilatation as illustrated in FIGS. 2 and 3.

Single layer balloons having the differential compliancy characteristicsdescribed above can also be provided using other balloon materials suchas polyethylene terephthalate (PET). For example, a one piece singlelayer PET balloon can be provided with a thinner wall in the focalsection compared to the one or two reference sections of the balloon.FIG. 6 discloses a schematic illustration of a balloon 50 in accordancewith this aspect of the present invention. The balloon 50 defines aninterior space 51 for containing inflation media as is understood in theart. The balloon 50 generally comprises a distal neck portion 52 andproximal neck portion 54 for securing the balloon 50 to the catheter. Aworking length of the balloon 56 extends between proximal shoulder 55and distal shoulder 57.

The working length 56 of the balloon 50 is provided with a proximalreference zone 62 and a distal reference zone 58, separated by a focalzone 60. As has been discussed in connection with previous embodiments,the balloon 50 can alternately be provided with only a single referencezone either 58 or 62, together with the focal zone 60. Preferably,however, both proximal and distal reference zones 62 and 58 will beutilized with a central focal zone 60.

The thickness of at least a portion of the balloon wall in the area offocal zone 60 is thinner than the wall thickness in the reference zones62 and 58.

In one embodiment of the single wall focal balloon of the presentinvention, the balloon comprises PET. The balloon has a working lengthof about 20 mm, and the proximal and distal reference zones 62 and 58each have a length of about 5 mm. The focal zone 60 has a length ofabout 10 mm. The first inflated diameter at 8 ATM is about 3.0 mm, andthe focal section inflates in vitro to about 3.5 mm at 16 ATM. The wallthickness in the area of reference zones 62 and 58 is about 0.001inches, and the wall thickness in the area of focal zone 60 is about0.0007 inches.

Whether the balloon comprises PET or other balloon materials known inthe art, a thinner focal section compared to the thickness at thereference section can be provided using a variety of techniques. Forexample, the PET balloon can be exposed to heat and stretched in thecenter portion to provide a relatively thinner wall than the endreference portions. Alternatively, the balloon can be heated at its endsto shrink the balloon thereby increasing the thickness of the materialin the regions exposed to heat.

Thinning a portion of the wall of the balloon by stretching the materialcan be accomplished in any of a variety of ways that will be apparent tothose of skill in the art, in view of the disclosure herein. One methodof reducing the wall thickness in the region of the focal zone involvesan axial elongation of the tubular balloon stock under the applicationof heat. In general, the present inventor has found that the percentreduction in wall thickness is roughly equivalent to the percent axialelongation of the tubular stock. Thus, the tube stock is axiallyelongated a sufficient distance to achieve the desired reduction in wallthickness.

In one application of the invention, a molded PET balloon having a wallthickness of about 0.001 inches was axially elongated a sufficientdistance to reduce the focal zone thickness to about 0.0007 inches. Amolded PET balloon having a wall thickness of about 0.0008 inches wasaxially elongated by 40% to produce a wall thickness of about 0.0005inches.

In one application of the method of the invention, a length of tubularpolymeric stock is provided. The stock may be cut to a useful workinglength, such as 10-20 centimeters. Excess stock length following theelongation process will be trimmed prior to mounting of the balloon onthe catheter shaft as will be understood by those of skill in the art.

A 15 cm length of PET balloon tubing having a wall thickness of about0.0010 inches and an inflated outside diameter of about 3.0 mm wasclamped at or near each end in a device configured to apply an axiallystretching force to the tubing. Prior to closing one of the clamps, aneedle was advanced through the open end of the tubing so that thetubing can be pressurized following clamping. Following clamping, thetubing was inflated under a pressure of about 100 psi, and axial tensionin the area of about 1 lb. was applied.

The foregoing setup for a 3 mm balloon was accomplished inside of a 3 mmcapture tube. First and second aluminum heat sinks were thermallycoupled to the capture tube, and spaced about 5 mm apart. A hot airheater having a length of about 5 mm in the axial tube direction waspositioned in between the heat sinks and advanced towards the capturetube to heat the capture tube. The heat sinks assist in localizing theregion of the tubing stock which will be heated by the heater, as willbe understood by those of skill in the art.

Upon reaching a temperature of about 200° F., the tube stock begins tostretch under the axial tension. The axial length of travel of thestretching clamps is preferably limited to provide a predetermined limitfor the percentage axial elongation. In one application of theinvention, the 5 mm heated section grew to about 5 or 7 mm in axiallength following a 20%-40% increase in the distance between the clamps.Any of a variety of modification to the foregoing procedure can bereadily envisioned by those of skill in the art. For example, alternatesources of heat such as forced air heating, infra red, electrical coil,and others known in the art can be used. In addition, stretching can beaccomplished through any of a variety of physical setups, which can bereadily assembled by those of skill in the art. Stretching without theapplication of heat, such as by cold rolling or cold forming a portionof tubular stock may also provide an acceptable thinning of the balloonwall for certain types of balloon materials.

Subject to the pressure retention characteristics of bonds betweendissimilar balloon materials, the balloon can alternatively be providedwith a relatively more compliant material in a focal section, and arelatively less compliant material in a reference section. Balloonshaving a combination of materials having different compliancies can bemanufactured, for example, using two extrusion heads which alternatelydrive balloon material through a single orifice. Any of a variety ofmaterial pairs may be used, such as nylons of different hardness, PETand PE, and others that can be selected by those skilled in the art. Asa further alternative, the focal section can be formed from an entirelydifferent balloon which is positioned adjacent a single referenceballoon or positioned in between two reference balloons to produce aballoon having some of the characteristics of the focal balloon of thepresent invention.

Balloons 18 made in accordance with the design illustrated in FIGS. 2and 3 have been found to exhibit the inflation pressure profileillustrated in Table 2.

                  TABLE 2                                                         ______________________________________                                                   CENTRAL                                                                       SEGMENT   PROXIMAL AND DISTAL                                      PRESSURE   DIAMETER  SEGMENT DIAMETER                                         ______________________________________                                         6 atm     2.5 mm    2.5 mm                                                    7 atm     2.6 mm    2.5 mm                                                    8 atm     2.7 mm    2.5 mm                                                    9 atm     2.8 mm    2.5 mm                                                   10 atm     2.9 mm    2.6 mm                                                   11 atm     3.0 mm    2.6 mm                                                   12 atm     3.1 mm    2.7 mm                                                   13 atm     3.2 mm    2.7 mm                                                   14 atm     3.2 mm    2.7 mm                                                   ______________________________________                                    

The inflation pressure profile of the variable diameter inflationballoon 18 illustrated in Table 2 provides an example of the manner inwhich a balloon 18 made in accordance with the foregoing method isinflated with the application of increased pressure. Initially, thecentral segment 30 and the proximal and distal segments 26, 28 of theballoon 18 inflate together in vitro as the pressure increases. When thepressure reaches 6 ATM, for example, the diameter of the proximal anddistal segments 26, 28 and the central segment 30 of the balloon allremain at about 2.5 mm. At 11 ATM, the diameter of the central segment30 of the balloon 18 has grown to about 3 mm while the proximal anddistal segments 26, 28 remained inflated to the first diameter ofapproximately 2.5 mm. The diameter of the central section 30 of theballoon 18 will continue to increase at least in vitro until the burstpressure of the balloon 18 is reached. In one prototype, the burstpressure was approximately 20 ATM at normal body temperature.

Both the first inflation diameter and the second inflation diameter canalso be varied depending upon the desired catheter characteristics aswill be understood by one of ordinary skill in the art. In a preferredembodiment, a first inflated diameter of the catheter for coronaryangioplasty applications is approximately 2.5 mm. Upon an increase ofpressure, this diameter grows to a second inflated diameter ofapproximately 3 mm in the central focal segment 30. In general, balloonscan be readily constructed having a difference between the firstinflation diameter and second inflation diameter anywhere within therange of from about 0.1 mm up to 1.0 mm or more, depending upon theelastic limits of the material from which the balloon was constructed.Typically, coronary angioplasty dilatation balloons will have a firstdiameter within the range of from about 1.5 mm to about 4.0 mm. Typicalballoons for use in peripheral vascular applications will have a firstinflation diameter within the range of from about 2 mm to about 10 mm.

Dilatation balloons can readily be constructed in accordance with thepresent invention in which entire length of the balloon from, forexample, proximal shoulder 42 to distal shoulder 46 (FIG. 2) is variablefrom a first inflated diameter to a second larger inflated diameter inresponse to increasing pressure. Alternatively, balloons in accordancewith the present invention can readily be constructed in which aproximal portion of the balloon is compliant so that it can grow inresponse to increased pressure, while a distal portion of the balloonhas a fixed inflated diameter. This configuration may be desirable, forexample, when the native vessel diameter is decreasing in the distalcatheter direction. Positioning the catheter so that the compliantportion is on the proximal (larger diameter) portion of the vessel mayminimize damage to the vessel wall in certain applications.Alternatively, the compliant segment can readily be positioned on thedistal end of the balloon with a substantially fixed inflated diametersegment on the proximal end of the balloon.

A variable diameter balloon 18 made in accordance with the foregoingdesigns has been found to benefit certain conventional percutaneoustransluminal coronary angioplasty (PTCA) procedures. In accordance withthe method of the present invention, the variable diameter balloon 18 ispercutaneously advanced and positioned such that the central segment 30of the balloon 18 is adjacent a vascular treatment site. Generally, thetreatment site is a stenosis such as due to a plaque or thrombus. Thevariable diameter balloon 18 is inflated to a first inflation profile tobegin dilation of the stenosis. Preferably, the first inflation profileis achieved by applying up to about 6 ATM of pressure to the balloon 18.At the first inflation profile, the entire balloon is inflated to theinner diameter of the vessel, thus restoring patency to the vascularlumen. In one embodiment, the variable diameter balloon 18 is inflatedto a first inflation diameter, of about 2.5 mm, at an inflation pressureof 6 ATM. The first inflation diameter is preferably about the nativediameter of the vessel.

As additional pressure is applied to the variable diameter balloon 18, asecond inflation profile is achieved wherein the central segment 30 ofthe balloon 18 expands beyond the diameter of the first inflationprofile to a second inflation diameter, while the proximal segment 26and the distal segment 28 remain at or substantially at the firstinflation diameter. As the pressure applied to the variable diameterballoon 18 increases, the diameter of the central segment 30 of theballoon 18 extends past the native diameter of the vessel to the secondinflation diameter. Utilizing this method, and depending upon theballoon size selected, the stenosis is compressed to a point which isbeyond the native diameter of the vessel. In a preferred embodiment, atan applied pressure of 11 ATM the diameter of the central segment 30 ofthe balloon 18 at the second inflation diameter is 3 mm and the diameterof the proximal end 26 and the distal end 28 at the first inflationdiameter is approximately 2.5 mm. Second inflation diameters in betweenthe first inflation diameter and the maximum inflation diameter can bereadily achieved by controlling inflation pressure, as illustrated forone embodiment in Table 2, above.

After the stenosis is compressed to or beyond the native diameter of thevessel, the balloon is evacuated and the catheter withdrawn.Alternatively, if desired, the pressure is reduced until the balloon 18resumes the first inflation profile. At this point, the balloon 18 maybe held at the first inflation diameter for short periods to continue tomaintain patency of the lumen if short term rebound is a concern. Thispost dilatation step is preferably accomplished using a catheter havingperfusion capabilities. Finally, the remaining pressure applied to theballoon 18 is reduced causing the variable diameter balloon 18 todeflate. The catheter is then extracted from the vessel utilizingconventional PTCA procedures.

The "focal" or "differential compliance" balloon of the presentinvention provides important real time diagnostic information about thelesion being treated. In a balloon having one or more noncompliant orsubstantially noncompliant zones such as proximal segment 26 and distalsegment 28 and a central focal segment 30, (FIG. 2) inflation within alesion will proceed through a series of discreet phases. The phases canbe visually differentiated by observing the balloon fluoroscopically andcomparing the apparent diameter of the central section with the diameterof the one or more substantially noncompliant zones. The substantiallynoncompliant zones may be considered reference zones for presentpurposes.

When the balloon 18 is inflated within a lesion, the reference zone willnormally be positioned proximally or distally of the lesion and thecentral zone will be centered within the lesion. As balloon inflationbegins, the overall balloon may take on a "dog bone" shape with thecentral portion radially inwardly restrained by the lesion. As inflationpressure is increased, the central section will tend to expand until theballoon has assumed an overall generally cylindrical profile. At acertain higher pressure, the balloon will focalize, such that thecentral region has reached its second, larger inflated diameter. Byobserving the first pressure at which the balloon assumes a generallycylindrical configuration and the second higher pressure at which theballoon focalizes, the clinician can learn important information aboutthe morphology of the lesion.

For example, in a balloon rated 3.0 mm at 6 atmospheres, the referencezone may grow to 3.2 mm at 11 atmospheres. The focal section will growto 3.0 mm at 6 atmospheres, and, in a healthy artery, should grow to 3.5mm at 11 atmospheres. If there has been no focalization at 11atmospheres, the clinician will know that the lesion is highly calcifiedor is otherwise highly resistant to expansion. The pressure can then begradually increased up to a maximum pressure which approaches the burstpressure, and the pressure at which focalization is finally visualizedwill reveal information about the degree of calcification or otherinformation about the lesion.

Thus, there is provided in accordance with the present invention amethod of obtaining characterizing information about a lesion. Thecharacterizing information is obtained by positioning a differentialcompliance balloon in the artery such that a central focal section ispositioned within the lesion. The balloon is inflated to a firstinflation pressure such that the balloon achieves a "dogbone"configuration with the lesion. The clinician preferably notes that firstpressure. The pressure is increased until the balloon achieves agenerally cylindrical exterior configuration. The pressure at which thesubstantially cylindrical configuration is achieved is preferably noted.The pressure in the balloon is increased further until focalization ofthe central section is achieved, and the focalization pressure is noted.One or more of the noted pressures may be compared to other informationconcerning the same patient or against reference data to assess thenature of the lesion. Since the balloon can be readily fluoroscopicallyvisualized, the clinician receives real time information about the sizeof the inflation balloon merely by visually comparing the focal sectionwith the reference section. If, at a particular pressure, the balloon is"straight across" (i.e. has not focalized) the clinician can look at thereference chart for the balloon or rely upon experience to assess thediameter of the vessel at the treatment site.

In accordance with another aspect of the present invention, there isprovided a method of interactive angioplasty using the differentialcompliance balloon of the present invention. In general, the interactiveangioplasty method involves inflating the balloon to a first inflationpressure, which should produce a first inflation profile for aparticular expected lesion morphology. If the profile of the balloon atthe first inflation pressure is different than the expected firstinflation profile, the clinician will know that the lesion morphologymay be different than anticipated. The clinician can thus responsivelychange the course of treatment, such as by removing the catheter andreplacing it with a different one.

For example, if a highly calcified or fibrotic lesion is expected andthe first inflation pressure produces a substantially cylindricalballoon rather than a dogbone shaped balloon, the clinician maydetermine that the balloon selected was too small or the lesion was notcalcified or fibrotic as expected. That balloon catheter may bewithdrawn and a catheter having a larger balloon thereafter positionedin the lesion. If the expected degree of inflation at the focal zone(compared, for example, to the reference zone) fails to occur at theexpected inflation pressure, the clinician may alternatively elect toincrease the inflation pressure, thereby exerting a greater force on thelesion.

Alternatively, lesion morphology information obtained by comparing theexpected inflation profile at a given pressure stage with the actualinflation profile may cause the clinician to seek alternate treatment,such as drug therapy, surgery, or other techniques that may be availableat the time. More rapid progression than expected from dogbone tocylindrical to focalized inflation may indicate the presence of softplacque or of a thrombosis, and measures can be taken in response tominimize the risk of over dilatation or embolization. These measures mayinclude drug therapy such as local administration of streptokinase orTPA, or other measures such as atherectomy, laser therapy or stenting.

One of the advantages of the interactive angioplasty of the presentinvention is that the clinician can alter the course of treatment duringthe procedure, in response to information obtained during the procedureabout lesion morphology or progression of the procedure. For example, ifthe balloon fails to focalize at the pressure previously expected toproduce focalization, depending upon other circumstances of the patient,the clinician may determine that further dilatation of the lesion willproduce an undesirable dissection of the artery, and a differenttreatment may be indicated. Alternatively, the clinician may elect tosimply increase the inflation pressure until focalization occurs, orsubstitute a different balloon having a different inflation diameter orcapable of sustaining a greater inflation pressure.

At each of the reference points identified previously herein, such asthe dogbone profile, the cylindrical profile, and the focalized profile,any deviation from the expected pressure to achieve that profile canthus be noted by the clinician and used to assess the course of furthertreatment. The interactive angioplasty method of the present inventioncan be accomplished both in the context of balloon dilatation and alsoin the context of implantation and or sizing of an intervascularprosthesis (stent).

Pressure response data for a series of exemplary balloons manufacturedin accordance with the present invention using techniques describedpreviously herein is provided in Table III below. The compliance curvesfor a reference zone and a focal zone of a differential complianceballoon rated for 3.5 mm at 6 atmospheres are illustrated in FIG. 5.

                  TABLE III                                                       ______________________________________                                        EFFECT OF INCREASED PRESSURE ON BALLOON DIAMETER                              Balloon     11 ATM   14 ATM      16 ATM                                       ______________________________________                                        3.0 mm                                                                        Reference Zone                                                                            3.2 mm   3.2 mm      3.3 mm                                       Focal Zone  3.5 mm   3.5 mm      3.5-3.7 mm                                   3.5 mm                                                                        Reference Zone                                                                            3.7 mm   3.7 mm      3.8 mm                                       Focal Zone  4.0 mm   4.0 mm      4.0-4.2 mm                                   4.0 mm                                                                        Reference Zone                                                                            4.2 mm   4.2 mm      4.3 mm                                       Focal Zone  4.5 mm   4.5 mm      4.5-4.7 mm                                   ______________________________________                                    

As exemplified in Table III, the reference zones on a particular balloonare expected to have a predetermined diameter at certain pressures. Forexample, the reference zones on a 3.0 mm balloon are expected to inflateto 3.2 mm at 11 ATM. If the balloon appears to be "straight across" at11 ATM, the clinician knows that the focal section and therefore thelesion has been inflated to 3.2 mm. If the balloon has focalized, theclinician knows that the lesion has been inflated to 3.5 mm by referringto a look up table containing the balloon specifications. Iffocalization does not occur until a higher pressure such as 14 ATM hasbeen reached, the clinician still knows that the lesion has beeninflated to 3.5 mm, but also knows that the lesion was relativelycalcified or fibrotic.

The present interactive angioplasty invention thus enables the clinicianto take into account the difference in balloon inflation characteristicsbetween the in vitro and in vivo environments. Balloons in vitro exhibita predictable inflation response to pressure. Balloon inflation in vivo,however, can be quite different from the balloon rating, and also fromlesion to lesion, as a result of the differences in vessel wallthickness, lesion morphology and other characteristics that affect theresistance to radial expansion in the area of the target lesion. Byproviding reference information such as the inflated diameter of thereference and focal zones of a balloon at each of a series of pressures,the clinician can determine the actual diameter of the balloon in thefocal zone by observing the balloon in either of the "straight across"or focalized inflation profiles.

The differential compliance balloon of the present invention is alsoparticularly suited for the implantation and or sizing of intravascularstents. For example, in a 3.2 mm vessel, it may be desirable to dilate astent to 3.5 mm inside diameter since some stents tend to recoil invivo. If the balloon is inflated up to 10 ATM with no focalization, theclinician knows to increase the pressure until a focal section becomesapparent. When the focal section has become apparent, the clinician willknow that the inside diameter of the stent has been appropriatelyinflated to 3.5 mm.

In accordance with a further aspect of the present invention, there isprovided a method of implanting a tubular stent within a body lumen.Tubular stents of the type adapted to be carried to a vascular site on aballoon catheter, and for expansion from a first insertion diameter to asecond implanted diameter are well-known in the art.

In accordance with the method of implanting a tubular stent, anexpandable stent is positioned about the deflated balloon of a variablediameter balloon catheter in accordance with the present invention. Theballoon is thereafter percutaneously inserted into the vascular systemand transluminally advanced to position the stent at the treatment site.The balloon is thereafter inflated to at least a first inflationconfiguration, wherein the balloon exhibits a substantially cylindricalprofile throughout its axial length. Thereafter, the balloon isoptionally inflated to a second inflation profile, thereby inflating atleast a portion of the stent to a second, greater diameter. Dependingupon the etiology of the underlying condition, the central region of thestent may preferentially be inflated to a larger diameter than either ofthe axial ends of the stent. Alternatively, the axial length of thestent is selected to approximately equal the axial length of the focalzone on the inflation balloon. In this manner, the inflation balloonwithin the stent is expandable to a diameter slightly larger than thenative diameter of the adjacent vessel. This permits subsequentovergrowth of endothelium along the interior wall of the stent whilestill leaving a lumen having an interior diameter within the stentapproximately equal to the native diameter of the lumen adjacent thestent.

In accordance with a further aspect of the present invention, thevariable diameter balloon is utilized to "tack down" a previouslypositioned tubular stent. In accordance with this aspect of the presentinvention, a tubular stent is identified within a body lumen. The focalballoon is positioned within the stent in accordance with conventionalPTCA procedures, and the balloon is inflated so that the central, focalsection enlarges the diameter of at least a first portion of the stent.The balloon is thereafter reduced in diameter, and, preferably,repositioned within a second region within the stent and then reinflatedto expand at least the second region of the stent. Expansions of thistype can be repeated until the stent has been expanded as desired. Theballoon is thereafter evacuated and removed from the patient.

In accordance with a further aspect of the present invention, there isprovided a method of percutaneous transluminal angioplasty in whichmultiple lesions of differing sizes are dilated without removing thecatheter from the body. In accordance with this aspect of the presentinvention, the variable diameter balloon is positioned within a firststenosis in accordance with conventional PTCA techniques. The balloon isdilated to a sufficient diameter to restore patency to the vascularlumen. The balloon is thereafter deflated, and repositioned within asecond stenosis in the vascular system. The balloon is inflated torestore patency of the vessel in the region of the second stenosis.Optionally, the balloon may be deflated, and repositioned within a thirdstenosis in the body lumen. The balloon is then inflated to a sufficientdiameter to restore patency in the body lumen in the region of the thirdstenosis. Four or more lesions can be treated seriatim in this manner.

Preferably, the balloon is inflated to a first diameter in the firststenosis, and to a second, different diameter, in the second stenosis.In this manner, multiple dilatations at different diameters can beaccomplished utilizing the balloon of the present invention. This methodis accomplished by supplying a first inflation pressure to the balloonwhile the balloon is positioned in a first position in the vascularsystem, and thereafter supplying a second pressure to the balloon whenthe balloon is in a second position in the vascular system. Inaccordance with the previous disclosure herein, each of the first andsecond inflation pressures is selected to achieve a preselectedinflation diameter of the balloon.

A number of the advantages of the interactive angioplasty methods andstent implantation methods of the present invention can also be accruedthrough the use of an alternate embodiment of the balloon of the presentinvention as illustrated in FIG. 7. Referring to FIG. 7, there isdisclosed a fixed focal balloon 64. By "fixed" focal balloon, it ismeant that the balloon assumes a stepped configuration in its initial invitro inflated profile. Increased inflation pressure beyond the pressurenecessary to achieve the initial stepped inflation profile does notappreciably change the relative proportionality of the profile from itsinitial stepped configuration.

The stepped configuration is characterized by a difference in diameterbetween at least one reference zone and a focal zone, preferably on thesame balloon. The fixed focal balloon of the present invention can beconstructed using either relatively compliant or relatively noncompliantmaterials, with the resulting characteristics that will be readilyapparent to those of skill in the art in view of the disclosure herein.Preferably, the fixed focal balloon comprises polyethyleneterephthalate.

The embodiment of the fixed focal balloon 64 illustrated in FIG. 7 has acentral focal zone and a proximal as well as a distal reference zone.However, the present inventors also contemplate fixed focal balloons inwhich either the proximal reference zone or the distal reference zone isomitted. These embodiments include only a single reference zone and asingle focal zone. The reference zone may be positioned eitherproximally or distally of the focal zone.

Alternatively, the proximal and distal zones in a three zone balloon maybe inflatable to the relatively larger diameter, while the central zoneis inflated to the smaller, reference diameter. This embodiment may beconsidered to have a proximal and a distal focal zone and a singlecentral reference zone. The desirability of one combination over anotherwill be governed by the requirements for a particular balloon dilatationor stent or graft implantation procedure as will be apparent to those ofskill in the art in view of the disclosure herein.

Referring to the embodiment illustrated in FIG. 7, the fixed focalballoon 64 is provided with a proximal reference zone 66, a centralfocal zone 68 and a distal reference zone 70. The relative lengths ofeach of these zones may vary considerably depending upon the intendeduse of the balloon. In general, any of the dimensions of the balloon,both in terms of diameters and lengths as well as other catheterdimensions, may be the same as those disclosed in connection with otherembodiments previously disclosed herein. In one particular application,the focal zone 68 has an axial length of 10 millimeters, and each of theproximal zone 66 and distal zone 70 has an axial length of about 5millimeters. At 8 atmospheres inflation pressure, the proximal referencezone 66 has an outside diameter of about 3 millimeters, and the focalzone 68 has an outside diameter of about 3.4 millimeters. The sameballoon at 18 atmospheres inflation pressure has an outside diameter ofabout 3.1 millimeters in the proximal reference zone 66 and an outsidediameter of about 3.5 millimeters in the focal zone 68. That particularballoon was constructed from PET, having a wall thickness of about0.0006-0.0008 inches.

Depending upon the desired clinical performance of the balloon, therelative expansion characteristics of the reference zone compared to thefocal zone can be varied. For example, although the focal section willnormally retain a larger inflated diameter than the reference zone, thereference zone may grow in response to an increase in inflation pressurea greater amount than the focal zone. In one PET balloon, having a wallthickness in the range of from about 0.0006 to about 0.0008 inches, thegrowth of the reference zone upon an increase in inflation pressure from8 to 18 atmospheres was about 0.2610 millimeters. The growth in thefocal zone over the same pressure increase was about 0.1457 millimeters.It may alternatively be desired to achieve a greater growth in the focalzone compared to the reference zone, or an equal growth in each zone asa function of increased pressure. Optimizing the growth response toincreased pressure of the focal zone relative to the reference zone forany particular intended application can be accomplished by the exerciseof routine skill in the art in view of the disclosure therein.

The fixed focal balloon 64 further comprises a first transition 72 whichsteps the diameter of the balloon up from the diameter of the cathetershaft 74 to the diameter of the proximal reference zone 66. All balloonshave some form of transition, such as first transition 72, and thereference zone 66 is to be distinguished from what is simply atransition, such as transition 72. Thus, the reference zone 66 isprovided with a visibly discernable generally cylindrical exteriorconfiguration in the inflated state, or other characteristic inflatedconfiguration, so that it can be distinguished visibly from thetransition 72 in vivo. Thus, the proximal reference zone 66 can beeither a cylindrical section which transitions sharply into a generallyconical transition section, such as first transition 72. Alternatively,the reference zone 66 may comprise a continuation of a first transition72, but with a visibly different angle with respect to the longitudinalaxis of the catheter when compared to the angle of the surface of thefirst transition 72 taken in the axial direction. In one embodiment ofthe invention, the surface of the first transition 72 measured in theaxial direction lies at an angle of approximately 20 degrees withrespect to the longitudinal axis of the catheter shaft 74.

A second transition 76 is provided to step the diameter of the inflatedballoon from that of the proximal reference zone 66 to the focal zone68. A third transition 78 is provided to step the outside diameter ofthe inflated balloon from the diameter of focal zone 68 down to thediameter of distal reference zone 70. The angle of each of the secondand third transition sections can vary depending upon desiredperformance and design characteristics, but in one embodiment of theinvention have a surface which lies on a plane extending in the axialdirection at an angle of about 11° from the longitudinal axis of thecatheter shaft 74. The axial length of each of the second transition 76and third transition 78 will vary depending upon the difference indiameter of the focal zone from the reference zone, but will generallybe within the range of from about 0.5 mm to about 4 mm.

A fourth transition 80 is provided to step the diameter of the balloon64 from that of the distal reference zone 70 back down to the diameterof the distal catheter shaft or tip 82.

The three zone embodiment illustrated in FIG. 7 can be produced havingany of a variety of dimensions, depending upon the particularcontemplated end use of the catheter. In the following nonlimitingexamples of balloon dimensions, the dimensions for the balloon arerecited at 8 atmospheres inflation pressure in an unrestrained (invitro) expansion.

For example, balloons can be readily provided having a focal zone 68inflatable to an initial inflation diameter of anywhere within the rangefrom about 1.5 mm to about 10 mm. For coronary vascular applications,the focal zone will normally be inflatable to a diameter within therange from about 1.5 mm to about 4 mm, with balloons available at every0.25 mm increment in between.

The reference zone, such as proximal reference zone 66 and/or distalreference zone 70 is preferably inflatable to a diameter within therange from about 1.25 mm to about 9.5 mm. For coronary vascularapplications, the reference zone is preferably inflatable to a diameterwithin the range of from about 1.25 mm to about 3.5 mm.

The focal zone is normally inflatable to a generally cylindricalprofile, which has a diameter that is greater than the diameter in thereference zone. Neither the focal zone nor the reference zone or zonesneed to be precisely cylindrical. Thus, the present invention can stillbe accomplished with some slight curvature or bowing of the surface ofthe focal zone or reference zone taken along the axial direction.

In general, the maximum diameter of the focal zone will be within therange of from about 7% to about 30% percent or more greater than theaverage diameter of the reference zone. Preferably, the maximum diameterin the focal zone will be at least about 10% greater than the averagediameter in the reference zone.

The configuration of the reference zone compared to the focal zone canbe varied considerably, as long as the reference zone and the focal zoneouter diameters can be visualized by the clinician using conventionalfluoroscopic or other visualization techniques. Thus, although thereference zone can take on a slightly conical configuration such that itramps radially outwardly in the direction of the focal zone, it shouldnot be to such an extent that the clinician cannot visuallydifferentiate the inflation profile of the focal zone compared to thereference zone in vivo.

The function of the reference zone, to provide a visual reference toindicate the relative inflation of the focal zone, can be accomplishedby the provision of radio opaque markers at either end of or within theballoon. For example, inflatable or flexible radio opaque markers may beprovided along the transition in a balloon from the catheter shaft tothe working zone in an appropriate position along the ramp such that,when the balloon is inflated, the radio opaque marker provides a visualindication of a predetermined diameter. Alternatively, the use ofradiopaque inflation media to inflate the balloon can also permit invivo visualization.

Although the preferred embodiments described above rely upon the balloonto provide a visual reference, the objectives of the present inventionmay be accomplished using other visual indica which will permit theclinician to assess the relative in vivo inflation of the focal zone.Thus, in a broad sense, the invention contemplates a visualizable aspectassociated with the focal section and a visualizable reference indicasuch as the balloon, a radiopaque marker on or associated with theballoon, radiopaque inflation media, or others, which allows theclinician to compare the diameter of the focal section relative to someother visual reference.

In addition to the provision of a visual reference to allow theclinician to assess the inflated diameter of the balloon, the balloon ofthe present invention provides a way to focalize the balloon inflationenergy at a predetermined position along the balloon. The axial lengthof the focal section can be varied considerably, depending upon thedesired axial length along which inflation energy is to be focalized.For example, the axial length of the focal section may be anywherewithin the range of from about 0.5 cm to about 5.0 cm. For coronaryvascular applications, the axial length of the focal balloon willnormally be within the range of from about 0.5 cm to about 2.0 cm forperforming conventional PTCA. The axial length will normally be withinthe range of from about 0.5 cm to about 5 cm for implanting expandabletubular stents, depending upon the length of the desired stent.Normally, the axial length of the focal section will be greater than theaxial length of the stent.

A variety of focal balloon catheters of the present invention arepreferably available to the clinician having an array of different axialfocal lengths, so that a balloon having the appropriate focal length canbe selected at the time of the procedure based upon the nature of theprocedure to be performed, and the location in the vasculature. Forexample, in a curved portion of the artery, the clinician may wish tominimize the axial length of the focal zone to the extent possible whilestill having a sufficient axial length to accomplish the dilatation orstent implantation procedure. An excessive axial length in the inflatedballoon for a given curved vessel can elevate the risk of vasculardissection as is well known in the art.

The axial length of the reference zone can also be varied considerably,depending upon the desired performance characteristics. In general, ithas been found that axial lengths of at least about 3 mm allow readyvisualization by the clinician. Axial lengths much shorter than 3.0 mmmay require too much effort to observe under fluoroscopic conditions,and the reference function of the reference zone may thus not be readilyaccomplished.

In one embodiment of the invention, produced in accordance with thethree-zone illustration of FIG. 7, the proximal and distal referencezones each have an axial length of about 5.0 mm and an inflated diameterof about 3.0 mm at 8 ATM. The axial length of the focal zone, includingthe length of the second transition 76 and third transition 78, is about8 mm. The diameter of the focal zone at 8 atmospheres inflation pressureis about 3.5 mm.

The fixed focal balloon 64 can be manufactured using any of a variety oftechniques which will be understood to those of skill in the art. Forexample, the balloon can be manufactured by blowing suitable tubingstock into a stepped mold cavity. Alternatively, the tubing stock can beblown into a first mold having a diameter approximately equivalent tothe reference diameter. The balloon can then be blown into a second moldhaving a larger diameter section corresponding to the focal section inthe finished balloon. The balloon is inflated into the larger mold underthe application of heat, as will be understood by those of skill in theart.

The fixed focal balloon 64 of the present invention or other fixed focalballoons as described herein can be utilized in any of the methodsdescribed in connection with the differential compliance balloons of thepresent invention. Thus, the real-time diagnostic information about thelesion which is obtainable through the use of the focal or differentialcompliance balloons described in connection with FIGS. 1-6 herein canalso generally be achieved using the embodiment of FIG. 7. Unlessclearly specified to the contrary, the various methods of the presentinvention, including both the differential compliance and stentimplantation and sizing methods, are intended to be accomplished byeither the fixed focal balloon or the variable focal balloon embodimentsof the methods of the present invention.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. A focalized balloon stent implantation catheter,comprising:an elongate flexible tubular body; an inflatable balloon onthe tubular body, having a proximal segment, a central segment, and adistal segment; and an expandable tubular stent removably positioned onthe balloon; wherein the central segment is inflatable to a greaterinflated diameter than either of the proximal segment and the distalsegment, thereby permitting expansion of the stent such that a centralportion of the stent is implanted with a greater inside diameter thanthe inside diameter of each of a proximal and a distal portion on thestent.
 2. A multiple zone balloon catheter, in combination with anexpandable intraluminal stent, comprising:an elongate flexible tubularbody; an inflatable balloon mounted on the tubular body; a first zone onthe balloon, inflatable to a first inflated diameter at a firstinflation pressure; a second zone on the balloon, inflatable to a secondinflated diameter at the first inflation pressure, said second inflateddiameter greater than said first inflated diameter; a third zone on theballoon, inflatable to the first inflated diameter at the firstinflation pressure, wherein the second zone is disposed intermediate thefirst zone and the third zone; and an expandable intraluminal stenthaving a central portion and end portions removably positioned on theballoon; wherein inflation of the balloon enlarges the diameter of thestent such that a central portion of the stent has a diameter that isgreater than the diameter of the end portions of the stent.
 3. Amultiple zone balloon catheter as in claim 2, wherein the axial lengthof the second zone is within the range of from about 5 mm to about 50mm.
 4. A multiple zone balloon catheter as in claim 3, wherein the axiallength of each of the first and third zones is within the range of fromabout 3 mm to about 25 mm.
 5. A multiple zone balloon catheter as inclaim 3, wherein the axial length of the second zone is within the rangeof from about 5 mm to about 20 mm.
 6. A multiple zone balloon catheteras in claim 2, wherein the maximum diameter of the second zone is withinthe range of from about 7% to about 30% greater than the averagediameter of the first zone.
 7. A multiple zone balloon catheter as inclaim 2, wherein the maximum diameter of the second zone is at leastabout 10% greater than the average diameter in the first zone.
 8. Amultiple zone balloon catheter as in claim 2, wherein the axial lengthof each of the first and third zones is at least about 3 mm.
 9. Amultiple zone balloon catheter as in claim 2, wherein the first andthird zones each have an axial length of about 5.0 mm and an inflateddiameter of about 3.0 mm at 8 atmospheres, and the second zone has anaxial length of about 8 mm, and a diameter at 8 atmospheres of about 3.5mm.
 10. A multiple zone balloon catheter as in claim 2, wherein saidballoon comprises polyethylene terephthalate.
 11. A multiple zoneballoon catheter as in claim 2, wherein the second zone is substantiallynoncompliant.